Consumer grade ballistic concrete testing

I have some super plasticizer need to make some samples with.

Does a residential concrete structure even need #5 or 6 rebar?
I was thing 3 and 4 and maybe some 5 for around corners and edges.

 

6 is common in walls and as vertical reinforcement in block walls, regardless of straight or corner.

 

What is your estimation for a reasonable number of pounds per yard for 4 and 6 inch walls?
If I'm going to build new it will likely have 6 inch concrete walls. But most people cast 4 inches.

 

I tested the stucco mesh lined sample.
The scenario is some one lines a form with stucco mesh and fills the form with medium workability 4,000psi concrete.
And talk about an unexpected result.

First shot damaged the surface, but didn't do much to the stucco mesh. Just kind of blasted away the sand and cement, left the big agg.
I tried to take a picture of the 2nd shot but it was a blur and didn't take a picture at shot number 3. So this is shot number 4.
4 shots barely cracked the sample slightly bulged the back side.


This is the back of the block after shot number 6, until shot 6 it was barely bulged and chipped.


So after taking 6 shots like a champ I figured I was going to be here a while, remember normally 3 shots spread evenly, or 2 shots really close to each other pulverizes a 4,000psi concrete control. So after shot 5 I started concentrating my fire to punch through.


Shot number 7 in the middle of the 6 shot area spalled the back, but the spalling didn't damage the blue foam under the sample. So depending on how you want to look at it this could be a failure.

Shot number 8 punched through and it would have sucked to have been standing behind where that round hit.


Then I shook out all the loose aggregate.


If I shot any other sample 8 times it would have been turned into aggregate.
So what the hell happened?
It appeared the stucco mesh contained the large aggregate much better than I expected. Normally the rounds just blasted away large chips of material. and the impact cracked the samples. Now most of the loose material hung around to disrupt the projectile and the stucco mesh would not allow cracks to allow the sample to fall apart. I turned over the sample after each test which dumped out a little loose material, could say that simulates being vertical.

Didn't some one say stucco mesh wouldn't help?
From 2 or 3 shots to failure to 7 or 8 shot and could have been more if I spread them out more till failure.
This is exactly why we test shit and don't just arm chair dictate reasons why something wont work. I figured it was going to help some, but nothing like this.
In my mind I had pretty much written off further testing or actually using stucco mesh in something until this test.

I have some more samples to blast, but I will consider my trigger finger itch scratched. For now.

Edit, I think I am going to try repairing this hole with some mortar and blasting it again.

 

FWIW and going by what I remember from quite a while ago, the pounds per yard is not a consideration for any reason besides cost estimation. To a very small degree, I had little interest in that, by the time I saw the stuff, it was already in the field and being placed. The design features specified the mesh and direction that the bar was supposed to be in. We did not check weights as long as the dimensions were right. Also for what it's worth, I've never seen a 4" cast wall, our minimums were 8 inch, residential and commercial. The main reason is for working space to get the rebar mats in and still have space to work a vibrator in between the forms and mats.

 

The standard specification on rebar requires a certain amount of space all the way around the bar.
example: you would want to put two 5/8" rebar 2" apart in a 4" wall. In South Louisiana a 6" wall with #5 (5/8")Rebar would suffice for wall construction with the proper footing (chain wall, foundation beam). if you use ICF you want have to layer foam on top of the ICF since it already has that in its design. MY BIGGEST PROBLEMS ARE STILL WINDOWS!!
The reason I suggested the stucco mesh and multi layering is so that your exterior veneer would increase the number of hits it could take before making it to the structure. Stucco is not a very strong product if placed only one layer to smooth out a wall. BUT, if used in multiple layer like a sandwich you can greatly increase its resistance. That over an ICF wall would be a tough wall to penetrate.
anytime you can put a space in between the layer you increase its resistance to penetration because that small gap will allow the primary energy impact to dissipate before striking the next layer. A good example would be to layer a couple of sheets of ply wood in two ways. One target stacked on top of each other and the other with 2" spacing between the sheets and then test to see if there is a difference in penetration.

 

Ratio is dependent on your maximum aggregate size. You would be better to you a 3/8 to 1/2 aggregate. The goal is to make the concrete as dense as possible. With smaller aggregates when the projectile hits the concrete it will only displace the aggregate by its max size so 3/8" aggregate equals a 3/8" displacement vs 1" aggregate leaving a 1" displacement.

 

I'm thinking with this stucco mesh test holding in most of the aggregate after the concrete sample was shot shows that bigger aggregate would be better, maybe?
If there is no stucco mesh to retain the loose material then smaller aggregate is probably better.

 

One layer of stucco mesh.

2 shots this close together has caused samples to fail with no reinforcement.


3rd shot cracked the sample. Normally the 3rd shot does them in. I took a picture of the back it was cracked and had a slight bulge but you cant see it in the picture I took.


The 4th shot just spread the damage on the front more and bulged the back a little more.

The 5th shot cracked the back pretty bad.


The 6th shot did it in and you can see the stucco mesh.

 

I took my forms apart and I am redoing them. No more cling film. Just heavy coats of polyurethane. I have one more test to do with the old form.
Next test form I am going to test add in fumed silica. I made a comment that you could be able to add plenty of fumed silica for $50 per yard. So I quantified that today.
I figure you should at least be able to get 2.5 gallons of fumed silica for $50. Which translates to about 12 volume ounces per cubic foot.
Or 1 and 1/3 ounce per test form, or 1/3 of a half cup.

Next weeks tests will have two 4,000psi control samples and the vacuum concrete samples to blast.

 

One of many form release agents to save on the plastic film..
DUOGARD - VOC Compliant Form Release Agent - W. R. Meadows

 

Great idea - much like the angled surfaces you see on some bunkers and even tanks. Deflect the energy away from the impact point, then in this case use other material to dissipate it. Nice.

 

The angled thing, I like it, I probably will test that.
Just have to invent a good way to go full scale.
If not it would be a good candidate for precast, because as I have stated before a very below average 720 square foot house could use 9 yards of concrete to make 4 inch walls and have an outer surface area of around 970 square feet of forms. That's a crap ton a forms to make rippled. If you did one wall at a time that's still 243 square feet if all 4 walls are equal.

I have a bunch of angle scrap in the back yard and could make a 12x12 test forms no problem. I think if I make a 1.75 inch average equivalent, the thin sections of the sample will be 2.25 on the peak and only 1.25 on the valleys with 2x2 angle. A hit on the thin section will just blow it apart.

I think if you want to do ripples on a 4 inch wall where code is 4 inches, at the thinnest point the wall still has to be 4 inches.
So the test metric will be 1.75 at the thinnest part, kind of like a 4 inch wall. But instead of 2x2 like you should probably use on a 4 inch wall I'm going to use 1x1 angle, because this is small scale.

 

Another test I would like to try, the old way of increasing strength of concrete was just to add more Portland cement.
Since my testing standard is 4,000psi concrete, or a "6 sack mix" (where you use 6 sacks of Portland cement weighing 94lb each to make each yard of concrete).
In the old days they would just dump in another sack of Portland cement to each yard. Turning 4,000psi 6 sack mix into 5,000psi 7 sack mix.
I figure for an added cost of about $14 per yard I have to test this.

Then a little math later I was able to figure that adding about 1 pound of Portland cement to a 50lb bag should convert it from 6 sack to 7 sack mix. Since one 50lb bag is 0.3 cubic feet, then it takes 90 bags to make a cubic yard. A sack of Portland cement is 94 lb so I'll just round it to adding 1lb of Portland cement to a 50lb bag.
Then of course for $20 to $28 per yard I will test something like a 7.5 to 8 sack mix. At some point too much Portland cement makes the concrete weaker.
My WAG (wild ass guess) is that reinforcement, adding something that is not a concrete ingredient like fiber, steel or plastic mesh to the concrete is going to be the winner.

The bagged 5,000psi concrete mix is about double the price of the standard 4,000psi mix. So it looks cost effective at this level.

 

Well the vacuum concrete was a spectacular failure.

The rounds landed closer than I wanted them to. I shot it a 3rd time in the middle of one of the halves and it broke too. No air entrapment allowed cracks to spread too easy?


This is why we do control samples.


The rounds hit almost identical to the vacuum concrete, but no broken sample.


Surely 3 shots does it in.
After the 3rd shot it was pretty much done. Note the large crack and the block halves moved when I turned it over.

This is what 3 shots did to the back.
Devastating cracks, imminent failure.

Shot number 4....

Science, fuk yeah, the letter c is sitting on top of the sample.
Another boring control test...




Normally after 3 shots the control samples are done. This one was too, just barely held together. That top left chunk moved when I picked up the sample. It was failed at this point but I still wanted to shoot it one more time. There was a little spalling on the back.



I have never blown a sample to bits so well as this one. I think luck was holding it together after the 3rd shot.

 

I poured 3 more samples today.
4,000psi with 1/4 cup of fumed silica, that's like adding $50 to $60 dollars per yard of fumed silica.
4,000psi supposedly converted to 5,000psi by adding some extra Portland cement.
And a 5,000psi cracking resistant mix control.

A few things I noticed about the 5,000psi cracking resistant stuff:
It has fiber, I already knew it did from previous usage.
I used my standard amount of water and it was too much. So this stuff has super plasticizers or water reducers already in it. It needs probably around 20% less water than the 4,000psi stuff.
It has a lot of aggregate.
The aggregate is sharper and angular, compared to 4,000psi concrete that had a lot of sand and smoother aggregate.
The 5,000psi crack resistant doesn't seem to have a lot of sand.
So it's the 5,000psi cracking resistant mix isn't just 4,000psi mix with a little fiber and a little more Portland cement for double the price, it's a completely different mix.

I am going to have to make another 5,000psi sample using a lot less water when the forms are clear.

 

I had a thought the other day that "left in place forms" like ICF would help the concrete cure better only because they are water tight and would only be open to the air at the top.
Then sure enough I found a vague reference to doing exactly that.
So I'm thinking make a sample like I always do, weighing up the concrete, (20.4lb) with 2 pounds of water, set it, weigh it again when it come out of the form 2 to 4 days later, put it in a large ziploc storage bag and add back any water weight lost over those 2 to 4 days which I estimate to be up to 0.3 pounds. Let it cure for 30 days. Maybe do some long term ones like that too.

 

Going back to the "adding Portland cement". The old legend is they would just add more cement.
I think 4,000psi concrete needs more Portland cement and aggregate to become 5,000psi.
Adding 1lb per of Portland cement to 50lb bag. But I think I should be adding athe least as much aggregate as cement to reduce the sand content of the final mix.

I don't want to use just any boring rounded aggregate. I'm going to use something like what's in the actual 5,000psi mix. Which i belive is something like crushed drainage rock, it's kind of big, sharp, pointy and around 3/4 inch. The drainage rock at Lowes is about 1 inch.
Testing and observations are leading me towards using larger aggregate anyway so that is fine.

I think my next test should be to add the equivalent of 1lb of Portland cement and up to 2lb of aggregate to a 50lb bag.
(But I don't want a whole 50lb bag just enough to make a sample)

Cost of adding more Portland cement and aggregate to a yard of concrete would be $14 for the cement and maybe $10 max for the aggregate if you only bought the aggregate in bags from the hardware store. The aggregate would cost almost nothing if sourced in bulk from an independent landscape supply place.